1. Field of the Invention
This invention relates to valves and, more particularly, to a valve used in the inlet or suction line of a rotary screw type compressor, between the compressor and the evaporator of a refrigeration system.
2. Description of the Prior Art
It has been recognized that in various kinds of refrigeration systems a valve means to control the flow from the evaporator into the compressor is desired. The necessity and purposes of valves in this part of the system have varied depending upon the nature and operation of the system. Thus, in the American Society of Heating, Refrigeration and Air Conditioning Engineers 1975 Equipment Handbook, page 20.11, there are illustrated suction pressure throttling valves which operate in response to various conditions to regulate the compressor suction pressure to a predetermined value.
In the patent to Post U.S. Pat. No. 3,788,776, there is disclosed an unloading control for a compressor which is responsive to discharge pressure for the purpose of throttling the inlet volume.
The patent to Persson et al U.S. Pat. No. 3,367,562, discloses a valve arrangement whose purpose is to modulate inlet pressure in order to maintain a constant discharge pressure. A time delay is disclosed for holding the inlet closed during starting.
In the patent to Andersson U.S. Pat. No. 2,069,808, a valve for regulating the pressure of gas flowing to a burner, or the like, is disclosed. It employs ordinary atmospheric pressure to close the inlet valve into a vacuum pump in order automatically to isolate the evacuated air during any shutdown of the vacuum pump. The structure includes a multiplicity of valve bodies, including for a strainer and with an independent positive shut-off.
The patent to Pellizzetti U.S. Pat. No. 3,633,380, discloses a valve in the suction line which is responsive to the output of the compressor and limits the input thereto in a modulating manner when the output exceeds a predetermined value. The valve has a pressure operating safety switch for stopping the compressor in the event of a loss of pressure, as might be caused by a leak.
The patent to Smith U.S. Pat. No. 3,722,228, discloses a dual valve assembly, one part in the inlet and the other part in the outlet port of the compressor. The valve is intended to close the inlet and outlet of a compressor during a shutdown.
The patent to Takahashi et al, U.S. Pat. No. 3,855,836, discloses a combination expansion valve and back pressure valve which is intended to regulate the refrigerant flow into an evaporator and maintain a fixed pressure therein. The valve is not directly responsive to compressor operation.